This invention relates to expandable prostheses, generally referred to as stents, which are adapted to be implanted into a patient""s body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. These devices are useful in the treatment of atherosclerotic plaque which develops in blood vessels, and is pretreated by angioplasty procedures, commonly referred to as percutaneous transluminal coronary angioplasty (PTCA) or an atherectomy which removes the plaque.
Stents are generally tubular-shaped devices which function to hold open a segment of a body lumen, blood vessel, or coronary artery. They are particularly suitable for use in supporting the vessel, holding back a dissected arterial lining which can occlude the fluid passageway, and are believed to be useful in reducing the likelihood of the development of restenosis.
Various means have been described to deliver and implant stents. One method frequently described for delivering a stent to a desired intraluminal location includes mounting and crimping the expandable stent on the expandable member of a catheter, such as a balloon, which is provided on the distal end of a catheter. The catheter is advanced to the desired location within the patient""s body lumen and the balloon is subsequently inflated to expand the stent into a permanent expanded condition and then the balloon is deflated and the balloon and catheter removed from the body lumen leaving the stent permanently implanted.
Another method frequently described for delivering a stent to a desired intraluminal location includes mounting the stent on the distal end of a catheter, where the stent is a self-expanding stent formed from self-expanding stainless steel, or the so-called shape memory alloys such as nickel titanium (NiTi). The self-expanding stents are implanted by advancing the catheter to the desired location within the patient""s body lumen, withdrawing a sheath so that the stent can self-expand into the body lumen, and then withdrawing the catheter and sheath leaving the stent permanently implanted. One of the difficulties encountered in using these prior art stents is the ability to tightly crimp the stent either on the balloon portion of the catheter or onto the distal end of the catheter. It is desired to have a low profile for delivery purposes yet be able to expand the stent to various diameters to hold open the vessel after implanting.
What has been needed and heretofor unavailable is a stent that can be crimped to a very small diameter thus reducing the profile of the stent as it is delivered through the vascular system, yet be able to expand to a wide range of diameters and yet maintain sufficient wall coverage of the vessel wall and maintain enough radial strength to hold open the body lumen into which it is expanded. The present invention satisfies this need.
The present invention is directed to a stent which is relatively flexible along its longitudinal axis to facilitate delivery through tortuous body lumens, but which is stiff and stable enough radially in an expanded condition to maintain the patency of the body lumen, such as a coronary artery, when implanted therein. The stent of the present invention is configured such that it can be crimped or reduced to a low profile, yet be expanded radially to any number of diameters yet maintain sufficient mechanical strength and radial support to hold open the body lumen into which it is expanded.
The stent of the invention generally includes a plurality of rings which are relatively independent in their ability to flex relative to one another. Interconnecting links (or struts) extend between adjacent rings to provide increased stability and are positioned so that the stent remains longitudinally flexible in all directions. At least some of the rings have curved sections attached to substantially straight arms where the arms have an expandable slit formed therein. The stent of the invention typically has a delivery configuration diameter, that is it is mounted on a catheter and tightly crimped thereon if it is of the expandable type, and is tightly pressed onto a catheter and covered with a sheath if it is of the self-expanding type. The expandable slits formed in the arms of the cylindrical rings permit the stent to be tightly crimped onto the catheter, and when expanded, the slits provide openings or apertures that allow the stent to expand radially outwardly and more evenly distribute bending stresses throughout the stent. Further, the openings in the arms provide better wall coverage than if the openings were not there.
In one embodiment of the invention, the stent is formed of a plurality of cylindrical rings, at least some of the rings having curved sections attached to substantially straight arms. The stent is formed of a deformable material so that it is mounted on the balloon portion of a catheter of either the rapid-exchange or over-the-wire type. At least some of the arms have an expandable slit formed therein, so that as the stent is expanded from a first delivery diameter to an expanded and implanted diameter, the slits open up to form holes or apertures. The cylindrical rings are interconnected by a plurality of links which are positioned so that the stent has uniform flexibility throughout its length. Alternatively, the arms are curved and have an expandable slit.
In another embodiment of the invention, the stent is formed of a plurality of rings, wherein at least some of the rings have curved sections attached to substantially straight arms, the arms having a slit formed therein. The rings are attached to each other by a plurality of links. In this embodiment, the stent is formed from a shape memory alloy, such as, for example, nickel titanium or nickel-titanium-vanadium. Typically, the stent is retained on the distal portion of a catheter of either the rapid-exchange or over-the-wire type, by a retractable sheath. The stent of the invention will expand from its delivery diameter to its expanded diameter when the sheath is removed or retracted proximally. Upon expansion, the slits in the arms of the cylindrical rings will expand to form openings or apertures. Alternatively, the arms are curved and have an expandable slit.
In another embodiment of the invention, the stent is formed of a plurality of rings, wherein at least some of the rings have curved sections attached to substantially straight arms, the arms having a slit formed therein. The rings are attached to each other by a plurality of links. In this embodiment, the stent is formed from a low memory metal, such as stainless steel, that is plastically deformed when expanded from a delivery diameter to an expanded diameter when implanted in a body lumen, such as a coronary artery. Typically, the stent is mounted on the balloon portion of a catheter, either of the rapid-exchange or over-the-wire type, and the balloon portion expands radially outwardly to expand the stent into contact with the body lumen. Upon expansion, the slits in the arms of the cylindrical rings will expand to form openings or apertures. Alternatively, the arms can be curved and have an expandable slit as well.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.